JPH04275715A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain a device in which strength is increased, the occurrence of crack is prevented and reliability is high by using a dielectric substrate obtained by means of coating glass on an allumina substrate in specified thickness. CONSTITUTION:The piezoelectric substrate obtained by forming a ZnO thin plate becoming a piezoelectric thin film on the dielectric substrate 2 is used. Interdigital transducers 4 and 5, either of which becomes an input-side and the other becomes an output-side, are provided on an interface between the dielectric substrate 2 and the ZnO thin film 3. The dielectric substrate 2 obtained by coating glass 7 on the allumina substrate 6 in the thickness of more than a wavelength lambda and less than 3lambda.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device using a piezoelectric substrate having a piezoelectric thin film formed on a dielectric substrate.

0002

2. Description of the Related Art A surface acoustic wave device of interest to the present invention has the following structure.

That is, a glass substrate is used as a dielectric substrate, and a piezoelectric substrate is used on which a ZnO thin film as a piezoelectric thin film is formed. An interdigital transducer made of aluminum, for example, is provided on the interface between the glass substrate and the ZnO thin film. A surface acoustic wave device having such a structure is usually molded with resin with a gap formed so as not to hinder the generation and propagation of surface acoustic waves in the piezoelectric substrate.

0004

SUMMARY OF THE INVENTION However, the surface acoustic wave device having the above structure has the following problems.

[0005] That is, the glass constituting the glass substrate has low tensile strength and is susceptible to cracks due to mechanical impact or thermal stress caused by soldering for terminal attachment.

[0006] Furthermore, the surface of the glass substrate opposite to the surface on which the ZnO thin film is formed is coated to prevent the generation of bulk waves.
It must be roughened by sandblasting, and the process for that is complicated.

[0007] Although it is conceivable to use such a high-strength alumina substrate instead of a glass substrate with low tensile strength, the ZnO/alumina structure has a large velocity dispersion of surface acoustic waves and does not work as designed. Unable to obtain filter characteristics.

Therefore, an object of the present invention is to solve the above-mentioned problems in a surface acoustic wave device using a piezoelectric substrate in which a piezoelectric thin film is formed on a dielectric substrate.

[0009]

[Means for Solving the Problems] The present invention provides a surface acoustic wave device in which a piezoelectric thin film is formed on a dielectric substrate, and an interdigital transducer is provided on the interface between the dielectric substrate and the piezoelectric thin film. It is something that is directed towards
In order to solve the above-mentioned technical problem, the dielectric substrate is made of glass on an alumina substrate with a thickness of λ or more and 3λ or less (λ:
It is characterized by the use of a coating with a thickness of 300 nm (wavelength).

0010

According to the present invention, a smooth surface is provided by glass coating, and velocity dispersion is not affected by the alumina substrate. Additionally, the lack of strength of glass is compensated by the alumina substrate.

In the present invention, the thickness of the glass to be coated is selected to be in the range of λ to 3λ (λ: wavelength) because if it is less than λ, the influence of the alumina substrate will be large, and for example, the thickness of the glass to be coated will be On the other hand, when it exceeds 3λ, the problem caused by the low tensile strength of glass becomes noticeable, as in the conventional case where a glass substrate is used as a dielectric substrate. Because it will appear.

0012

Therefore, according to the present invention, since an alumina substrate coated with glass to a predetermined thickness is used as the dielectric substrate, the strength is increased compared to the case where a conventional glass substrate is used. Cracks are prevented from occurring. Furthermore, due to the glass coating having a predetermined thickness, the velocity dispersion is not affected by the alumina substrate. Therefore, a highly reliable surface acoustic wave device can be provided.

[0013] Furthermore, by increasing the surface roughness of the alumina substrate to a certain extent before coating with glass,
There is no need for the sandblasting process that was conventionally performed to suppress bulk waves when glass substrates were used. Therefore, the number of manufacturing steps can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view showing a surface acoustic wave device according to an embodiment of the present invention. More specifically, a surface acoustic wave filter 1 is shown in FIG.

This surface acoustic wave filter 1 uses, as a piezoelectric substrate, a dielectric substrate 2 on which a ZnO thin film 3 serving as a piezoelectric thin film is formed. is provided with interdigital transducers 4 and 5, one of which is on the input side and the other is on the output side.

The feature of the present invention lies in the material and structure of the dielectric substrate 2. That is, as the dielectric substrate 2, the glass 7 is placed on the alumina substrate 6 in a range of λ or more and 3λ or less (λ: wavelength).
A coating with a thickness of . In order to coat the alumina substrate 6 with the glass 7, a process called glaze process is usually performed. It is preferable that the surface 8 of the alumina substrate 6 be roughened to some extent before such glazing treatment is performed.

In this embodiment, the drawer portions 9, 10, 11 of each of the interdigital transducers 4 and 5 are
, 12 are through-hole electrodes 13, 14, 1, respectively.
5 and 16, and electrical connection with the outside is achieved via these through-hole electrodes 13-16. Note that the through-hole electrodes 13 to 16 are illustrated as semi-cylindrical, but this is due to the method of manufacturing the surface acoustic wave filter 1. That is, the chip-shaped surface acoustic wave filter 1 is actually obtained by cutting a parent substrate on which a large number of surface acoustic wave filters 1 are formed, and at the stage of such a parent substrate, there are no through-hole electrodes. 13 to 16 are cylindrical. Since the cutting from the parent substrate is carried out so as to divide the cylindrical through-hole electrode into two, the surface acoustic wave filter 1 obtained by cutting includes the semi-cylindrical through-hole electrodes 13 to 16. will be formed.

In this way, through-hole electrodes 13 to 16
is formed, the drawer parts 9 to 12 can be connected by soldering.
The process of attaching terminals to each is no longer necessary,
The efficiency of manufacturing the surface acoustic wave filter 1 can be improved.

The surface acoustic wave filter 1 can be manufactured, for example, by the following procedure. That is, first, an alumina substrate 6 is prepared, and a coating of glass 7 is applied thereon by glazing treatment. Interdigital transducers 4 and 5 are then formed on glass 7 by depositing aluminum and patterning it using photolithography. Next, through-hole electrodes 13 to 16 are formed, and ZnO thin film 3 is formed to cover interdigital transducers 4 and 5. Note that the order of forming the through-hole electrodes 13 to 16 and forming the ZnO thin film 3 may be reversed.

The surface acoustic wave filter 1 may be provided with a resin exterior as in the conventional case, but preferably, as shown in FIG. 2, a cap 17 made of alumina is packaged instead of the resin exterior. It may also be used as part of a member. The cap 17 has a recess 18 on its lower surface, and is bonded to the dielectric substrate 2 using, for example, epoxy resin while avoiding contact with the interdigital transducers 4 and 5 (FIG. 1).

In this way, the cap 1 made of alumina
7, the cap 17 and the alumina substrate 6 can form an exterior. Since the cap 17 is made of alumina, which is the same as the alumina substrate 6, the expansion coefficient is small and the same as that of the alumina substrate 6, so that it can be bonded to the dielectric substrate 2 with high reliability. Furthermore, since the alumina substrate 6 can function as a part of the exterior, the packaged surface acoustic wave filter 1 can be made lower in height.

FIG. 3 is a diagram showing an example of frequency characteristics obtained by the surface acoustic wave filter 1 described above. This figure shows a case where the thickness of the glass 7 is 80 μm (λ=47 μm). As can be seen from this figure, the passband characteristics necessary for the filter are obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a surface acoustic wave filter 1 according to an embodiment of the present invention.

2 is a perspective view showing a state in which a cap 17 is attached to the surface acoustic wave filter 1 shown in FIG. 1. FIG.

3 is a diagram showing an example of frequency characteristics obtained by the surface acoustic wave filter 1 shown in FIG. 1. FIG.

[Explanation of symbols]

1 Surface acoustic wave filter (surface acoustic wave device) 2 Dielectric substrate 3 ZnO thin film (piezoelectric thin film) 4, 5 Interdigital transducer 6 Alumina substrate 7 Glass

Claims (1)

[Claims] Claim 1: A piezoelectric thin film is formed on a dielectric substrate,
In the surface acoustic wave device in which an interdigital transducer is provided on the interface between the dielectric substrate and the piezoelectric thin film, the dielectric substrate is a glass plate on an alumina substrate with a thickness of λ or more and 3λ or less (λ: wavelength). A surface acoustic wave device characterized by using a surface acoustic wave device coated with